Many occupations can potentially expose an individual to electrical arc flash and/or flames. Workers who may be exposed to accidental electric arc flash and/or flames risk serious burn injury unless they are properly protected. To avoid being injured while working in such conditions, these individuals typically wear protective garments constructed of flame resistant materials designed to protect them from electrical arc flash and/or flames. Such protective clothing can include various garments, for example, coveralls, pants, and shirts. Standards have been promulgated that govern the performance of such garments (or constituent layers or parts of such garments) to ensure that the garments sufficiently protect the wearer in hazardous situations. Fabrics from which such garments are constructed, and consequently the resulting garments as well, are required to pass a variety of safety and/or performance standards, including ASTM F1506, NFPA 70E, and NFPA 2112.
ASTM F1506 (Standard Performance Specification for Flame Resistant and Arc Rated Textile Materials for Wearing Apparel for Use by Electrical Workers Exposed to Momentary Electric Arc and Related Thermal Hazards, 2015 edition, incorporated herein by reference) requires arc rating testing of protective fabrics worn by electrical workers. The arc rating value represents a fabric's performance when exposed to an electrical arc discharge. The arc rating is expressed in cal/cm2 (calories per square centimeter) and is derived from the determined value of the arc thermal performance value (ATPV) or Energy Breakopen threshold (EBT). ATPV is defined as the arc incident energy on a material that results in a 50% probability that sufficient heat transfer through the specimen is predicted to cause the onset of second-degree burn injury based on the Stoll Curve. EBT is the arc incident energy on a material that results in a 50% probability of breakopen. Breakopen is defined as any open area in the material at least 1.6 cm2 (0.5 in.2). The arc rating of a material is reported as either ATPV or EBT, whichever is the lower value. The ATPV and EBT is determined pursuant to the testing methodology set forth in ASTM F1959 (Standard Test Method for Determining the Arc Rating of Materials for Clothing, 2014 edition, incorporated herein by reference), where sensors measure thermal energy properties of protective fabric specimens during exposure to a series of electric arcs.
NFPA 70E (Standard for Electrical Safety in the Workplace, 2015 edition, incorporated herein by reference) offers a method to match protective clothing to potential exposure levels incorporating Personal Protective Equipment (PPE) Categories. Protective fabrics are tested to determine their arc rating, and the measured arc rating determines the PPE Category for a fabric as follows:                PPE Category and ATPV        PPE Category 1: ATPV/EBT: 4 cal/cm2         PPE Category 2: ATPV/EBT: 8 cal/cm2         PPE Category 3: ATPV/EBT: 25 cal/cm2         PPE Category 4: ATPV/EBT: 40 cal/cm2 Thus, NFPA 70E dictates the level of protection a fabric must possess to be worn by workers in certain environments.        
NFPA 2112 (Standard on Flame-Resistant Garments for Protection of Industrial Personnel Against Flash Fire, 2012 edition, incorporated herein by reference) governs the required performance of industrial worker garments that protect against flash fires. Both NFPA 2112 and ASTM F1506 require that the garments and/or individual layers or parts thereof pass a number of different performance tests, including compliance with the thermal protective requirements of having a char length of 4 inches or less (NFPA 2112) or 6 inches or less (ASTM F1506) and of having a two second (or less) afterflame (NFPA 2112 and ASTM F1506), when measured pursuant to the testing methodology set forth in ASTM D6413 (Standard Test Method for Flame Resistance of Textiles, 2015 edition, incorporated herein by reference).
To test for char length and afterflame, a fabric specimen is suspended vertically over a flame for twelve seconds. The fabric must self-extinguish within two seconds (i.e., it must have a 2 second or less afterflame). After the fabric self-extinguishes, a specified amount of weight is attached to the fabric and the fabric lifted so that the weight is suspended from the fabric. The fabric will typically tear along the charred portion of the fabric. The length of the tear (i.e., the char length) must be 4 inches or less (ASTM 2112) or 6 inches or less (ASTM F1506) when the test is performed in both the machine/warp and cross-machine/weft directions of the fabric. A fabric sample is typically tested for compliance both before it has been washed (and thus when the fabric still contains residual—and often flammable—chemicals from finishing processes) and after a certain number of launderings (e.g., 100 launderings for NFPA 2112 and 25 launderings for ASTM F1506).
NFPA 2112 also contains requirements relating to the extent to which the fabric shrinks when subjected to heat. To conduct thermal shrinkage testing, marks are made on the fabric a distance from each other in both the machine/warp and cross-machine/weft directions. The distance between sets of marks is noted. The fabric is then suspended in a 500 degree Fahrenheit oven for 5 minutes. The distance between sets of marks is then re-measured. The thermal shrinkage of the fabric is then calculated as the percentage that the fabric shrinks in both the machine/warp and cross-machine/weft directions and must be less than the percentage set forth in the applicable standard. For example, NFPA 2112 requires that fabrics used in the construction of flame resistant garments exhibit thermal shrinkage of no more than 10% in both the machine/warp and cross-machine/weft directions.
In the electrical safety market, there is a need for flame resistant fabrics that achieve a high arc rating/fabric weight ratio while still complying with all applicable thermal protective requirements. More specifically, there is a need for lighter weight protective fabrics that achieve NFPA 70E PPE Category 2 protection (≥8 cal/cm2 arc rating). Due to high temperature working conditions in some workplaces, end users also have a need for comfortable (e.g., breathable) protective fabrics that have excellent moisture management properties (e.g., wicking).